Wildlife Habitat Connectivity · random-walk models • Resistance measures can be used in graph-theory applications From: McRae et al. 2008. Using Circuit Theory to Model Connectivity

Wildlife Habitat Connectivity: an overview

Peter Singleton USDA Forest Service, PNW Research Station

Brad McRae

The Nature Conservancy

Wildlife Habitat Connectivity: 1. What is habitat connectivity?

2. How do we assess connectivity?

3. Lessons learned by the Washington Wildlife

Habitat Working Group.

1. What is habitat connectivity?

Some definitions:

• Habitat: the resources and conditions present in an area that produce occupancy – including survival and reproduction – by a given organism. For example; food, water, shelter, space, and security.

• Connectivity: the state or extent of being joined or linked together.

• Habitat Connectivity: • The degree to which the landscape impedes or facilitates movement

among resource patches (Taylor et al. 1993).

Two components of connectivity:

• Structural: the structural characteristics or arrangement of patches on the landscape

• Functional: the specific ecological processes that flow through the landscape


Peshastin watershed, Chelan Co., Washington

Figuring out the relationship between landscape structure and landscape function: • Habitat: the resources and conditions present in an area that produce occupancy

– including survival and reproduction – by a given organism.

• Food

• Water

• Shelter

• Security

• Space

Barred owl breeding home range near Lake Wenatchee, WA.


Types of animal movement: • Intra-territorial: foraging, patrolling, “putting together the habitat pieces”

• Migration: regular movements between seasonally occupied portions of an

animal’s range

• Inter-territorial: relatively long-distance dispersal or exploratory movements, often associated with establishing a new home range

Barred owl home range Elk annual migration movement


dN/dt = cN(1-N)-eN N = number of patches at time t dN = change in occupied patches at t dt = change in time cN = number of patches colonized during t eN = number of patches that became extinct during t

In other words, the stability of a population is a function of the colonization and extinction rates of habitat patches supporting subpopulations.

Populations in well-connected landscapes are less likely to go extinct - Metapopulation dynamics:

Occupied Patches Extinct Patches


dN/dt = cN(1-N)-eN N = number of patches at time t dN = change in occupied patches at t dt = change in time cN = number of patches colonized during t eN = number of patches that became extinct during t

In other words, the stability of a population is a function of the colonization and extinction rates of habitat patches supporting subpopulations.

Occupied Patches Extinct Patches

Populations in well-connected landscapes are less likely to go extinct - Metapopulation dynamics:


Climate Change and Range Shifts:

Other Ecological Flows:

Migratory Movements:

Genetic Isolation:


Take-home messages:

• What “connectivity” means depends on the process or ecological flow of interest.

• Scale is really important.

• You have to think about all of this stuff in an evolutionary context: what conditions are the species or process adapted to?

• Always ask “connectivity for what?”


2. How do we assess connectivity?

What is the best analysis approach? Reasons we do landscape modeling: • To formalize or describe our current understanding about

patterns of structure or function within a landscape • To understand which environmental factors affect those patterns • To identify weaknesses in our understanding • To predict patterns in new geographies or in the future • To generate testable hypotheses about the patterns of interest

The principle of parsimony: Choose the simplest approach that can adequately answer the question at hand.

Complexity / Specificity

Unc

erta

inty

The Big Choice in Modeling…


Unc

erta

inty


Movement & Popn Simulation

Cost-weighted Distance

Circuit Theory

Patch Metrics


Unc

erta

inty


Movement & Popn Simulation


Circuit Theory

Patch Metrics


Resistance Surface Numbers indicate the resistance or energetic/risk ‘cost’ to move through cells. Typically based on a combination of land cover, human impact, and topography inputs.

Cost-weighted Distance Resistance Surface Numbers indicate the resistance or energetic/risk ‘cost’ to move through cells. Zeros are ‘source patches’.

Cost-weighted Distance Numbers indicate the minimum sum of ‘cost’ values between each cell and the most accessible source.

1 + 6 + 4 = 11


Least-cost Corridor Numbers indicate the minimum of the sum of ‘cost’ values for all possible routes between two sources that pass through a cell.

5 + 5 + 4 + 6 + 1 = 21


Least-cost Path The route between two sources with the lowest sum of ‘cost’ values.

5 + 3 + 7 + 1 + 1 = 17

• Based on electrical engineering theory

• Generates a measure of “flow” through each cell in a landscape

• Integrates all possible pathways into calculations

• Corresponds well with random-walk models

• Resistance measures can be used in graph-theory applications

From: McRae et al. 2008. Using Circuit Theory to Model Connectivity in Ecology, Evolution, and Conservation. Ecology.

Circuit Theory

A B

C D

E F Leas

t-cos

t pat

h di

stan

ce

R

esis

tanc

e di

stan

ce

Circuit Theory

Example: Tiger networks in central India

From: Dutta et al. 2015. Connecting the dots: mapping habitat connectivity for tigers in central India. Regional Environmental Change. DOI 10.1007/s10113-015-0877-z







• How to communicate biological meaning,

• What the products tell us,

• Credibility of modeled products,

• Willingness to “own” products they did not develop,

• Meeting the needs on multiple entities.

Photo: Sonia A. Hall

3. Lessons Learned from the WWHCWG: Challenges

Slide by Sonia Hall

1. Engage users from beginning to end,

2. Simplify, but don’t oversimplify,

3. Invest in interpretation,

4. Make all products freely available online,

5. Develop additional products tailored to users’ needs,

6. Shared vision and leadership.

Photo: Peter Prehn under CC BY-NC-ND 2.0

3. Lessons Learned from the WWHCWG: 6 Principles

Slide by Sonia Hall

Documents

Wildlife Habitat Connectivity · random-walk models • Resistance measures can be used in graph-theory applications From: McRae et al. 2008. Using Circuit Theory to Model Connectivity